On Saturday January 25th I held my first Bonsai Basics class aimed specifically at indoor growing. While I have mostly grown bonsai outdoors, I have dabbled in indoor growing over the past 10 years to get an idea of what the challenges are. For this first class, myself and four students held a discussion of how to address the challenges and increase our knowledge.
Some key points we considered for Indoor bonsai:
Species. While trees normally grow outdoors, it is possible to grow some species of trees that will thrive in an indoor environment as bonsai for years. Perhaps the single most important thing to recognize is that not all plants will tolerate this, and that the selection of species based on indoor conditions will have the greatest effect on success. Generally, tropical varieties that tolerate low humidity are what would grow best.
- Ficus nerifolia – willow leaf ficus
- Ficus benjimina
- Portulacaria Afra – a succulent type similar to Jade.
- Chinese Elm
- Lavender Star Flower – Grewia occidentalis
- Juniper – most types will not grow well.
- Atlas Cedar
Natural Light Quantity. For the Northern Hemisphere, (our discussion focused on the San Francisco Bay Area specifically) south-, west- and east-facing windows are all candidates for bonsai growing. If you have skylights near windows or kitchen windows that project outward to make a small greenhouse you’ll have even more light. North-facing windows will typically receive only indirect light, which may not be enough for many species.
Change of Sun angle during the year. The quality of light for a given window or placement within a house will change as the angle of the sun changes. While a south-facing window will receive a lot of light most of the year, during mid-summer the sun will track directly overhead and not shine directly in. Windows that face southwest or southeast will be more constant.
Ideal Positioning. Proximity to a light source means that ideal positioning should be explored and tweaked. The distance of the plant from the window will affect the radiant heat as well as the quantity of the light. For south-facing windows shading in the afternoon or morning by positioning the tree to the east or west is also a consideration.
Light diffusing. Direct sun coming through a window can be scorching to some plants. If you get full sun and your windows are not shaded, you may want to add a layer of diffusing material. Many older greenhouses use whitewash on the exterior of the roof to diffuse light. Consider scrim material as a diffusing option or just sheer curtain fabric. Think of this as the indoor equivalent of shade cloth.
Plant rotating. Unlike outdoors, the light source movement is restricted indoors – for even growth regular rotation of the plant in relation to the light source will lead to even growth on the front/back and sides of the plant. Rotate weekly 180 degrees or every few days 90 degrees.
The importance of Air
Air Temperature. For tropicals, the indoor air temperature between 65 and 75 will be nearly ideal. Keep in mind that air near a window can be significantly more variable than the air at your thermostat – use a thermometer positioned out of direct sunlight to measure the air temperature near your plants.
Air Movement. The inside of many houses has very little air movement. Because the metabolism of plants depends on gas movement out of tiny pores on the leaves, more air movement is better. Good air movement can reduce insect attacks, fungal problems and increase overall health. When possible, consider cracking open the window. Or, use a small fan.
Augmenting the environment
Supplemental Lighting. If you’re growing indoors and don’t have great natural light available you need supplemental lighting, yep that’s you basement apartment people! There are tons of lighting systems out there, and you’ll need to decide for yourself how much you want to spend initially, and the amount of time they stay on which affects your utility costs. The color temperature, type of bulb, positioning and duration/hours per day that you use all have an effect on the plants.
Supplemental Heating. Lighting sources can provide some heat, but generally it’s not in the ideal place – close to the leaf tips. Instead, consider seedling heating mats, these are inexpensive and gently warm the root zone. Of the three brands I have used, I prefer the HydroFarm brand for evenness of heat and toughness in the construction. Consider using a thermostat as well, which will automatically turn off the mat once the root zone reaches the programmed temperature.
Cooling. Anyone who has an air conditioner probably doesn’t have to worry about this, but if you don’t, note that when temperatures exceed 85 degrees you should be keeping a close eye on your plants for signs of stress.
Standard care applied to indoor growing.
Watering. Just like outdoor, you’ll have to stay on top of watering. Season, temperature, sun/lighting, plant metabolism and soil type among other things affect the frequency. Water when the soil is damp but before it dries out. Water based on the amount of moisture in the soil, not on a schedule, and when you do water, wet all the soil, either by soaking, overhead watering or alternating the methods.
Watering can be challenging because the plants either need to be placed in trays to catch the excess water, or transported away from wood furniture and other things that shouldn’t get wet. Use some sort of tray if you plan to water in place!
Fertilizer. Apply fertilizers on a regular basis. For indoor growing, organic fertilizer can cause smell and fly problems that are best avoided. Use a balanced mineral-based fertilizer either in liquid form (properly diluted!) or in the form of time-release pellets. There are many types that work, I use Dyna-Gro “Foliage Pro.” or “Bonsai Pro”
Pest Identification and Control. Pest problems indoors can be tricky to eliminate once a pest is established. If you don’t want to use chemistry on your indoor plants, first try spraying the pests off with water. Mixing soap with water and applying a spray to all leaf surfaces, and then rinsing it off will smother insects of many types. Consult IPM websites or pest specific advice and best practices. Be vigilant about pest control, as they can arrive in your house in a variety of ways. Check branch junctions, the under side of leaves and other hidden places regularly.
Good luck with your indoor adventures in growing!
Footnote: Some of the links above are affiliate links to Amazon.com. When you click on them, Amazon may track what you are doing, and if you buy anything I get something like 2 cents. (which I can then use to share my opinion with you more!)